Granular formations including open cell polystyrene particles

ABSTRACT

Closed-cell foamed polystyrene beads are shredded to form small size, open-celled foam particles. The particles are mixed with a slurry of a granulate and a liquid whereby the slurry enters the open cells to increase the density of the particles and suspend the particles in the slurry without floating the particles to the top. After an even distribution of the particles throughout the slurry is obtained the mixture is dried to form granulate objects, such as boards, having an even distribution of foamed polystyrene particles therein to reduce the density of the object.

nite States Patent [72] Inventor [54] GRANULAR FORMATIONS INCLUDING OPENCELL POLYSTYRENE PARTICLES Primary Examiner-Robert F. Burnett AssistantExaminer-Raymond O. Linker, Jr. Attorney-Townsend and Townsend ABSTRACT:Closed-cell foamed polystyrene beads are shredded to form small size,open-celled foam particles. The particles are mixed with a slurry of agranulate and a liquid whereby the slurry enters the open cells toincrease the density of the particles and suspend the particles in theslurry without floating the particles to the top. After an evendistribution of the particles throughout the slurry is obtained themixture is dried to form granulate objects, such as boards, having aneven distribution of foamed polystyrene particles therein to reduce thedensity of the object.

PLACE SHREDDED 2 Claims, 5 Drawing Figs.

[52] 11.8. CI 161/168, 156/39,161/1S9,161/162, 241/2, 241/3, 241/21 [51]1nt.Cl B32b5/l8 [50] Field ofSearch 161/159, 160,161,162,168;241/2, 3,21; 264/51, D16. 7; 156/34, 43

[5 6] References Cited UNITED STATES PATENTS 2,198,885 4/1940 Price161/159 EXPAND GRIND 8i SHRED POLYSTYRENE v BEADS POLYSTYRENE BEADSEXPANDED IN HIGH DENSITY PARTICLES SLURRY MIX PARTICLES 8i SLURRY TOSUSPEND PARTICLES SOLIDIFY SLURRY PATENTEDDEC28I97| INVENTOR.

IRBY H. LEACH FIG-I ATTORNEYS PATENTED HEE28 12m SHEET 2 [1F 3 Fl G3INVENTOR.

IRBY H. LEACH ATTORNEYS PATENTEU nines m1 3,530,820

SHEET 3 BF 3 PLACE SHREDDED EXPAND GRIND 8x SHRED PARTICLES POLYSTYRENEEXPANDED IN HIGH DENSITY BEADS POLYSTYRENE BEADS SLURRY MIX PARTICLESSOLIDIFY 8x SLURRY TO SLURRY SUSPEND PARTICLES F I G 4 FIG 5 INVENTOR.

IRBY H. LEACH BY TW "7W ATTORNEYS GRANULAR FORMATIONS INCLUDING OPENCELL POLYSTYRENE PARTICLES RELATED APPLICATIONS This application isrelated to the commonly owned, copending patent application bearing Ser.No. 844,896 filed July 25, 1969, for METHOD AND APPARATUS FOR SHREDDINGFOAM- BACKGROUND OF THE INVENTION It is now relatively common toincorporate lightweight particles into relatively high-density slurriedgranulate materials which are then formed and dehydrated into objectssuch as boards, moldings and the like. To the many desirablecharacteristics of the granulate, such as good thermal and acousticinsulating characteristics, fire resistance and low cost, the furtheradvantage of a reduced weight is added to facilitate the handling of thegranulate and reduce transportation costs.

In the past it has been common to incorporate polystyrene foam particlesinto a slurry of a granulate, such as gypsum, concrete or mortar forexample, and a liquid, usually water. The slurry is then agitated toevenly distribute the foam particles throughout the slurry. However, assoon as agitation ceases the buoyancy of the low-density foamedparticles floats the particles to the slurry top. This prevents theformation of an even slurry-foamed particle mixture, particularly sinceit usually takes several hours or days to dehydrate the slurry and drythe granulate into solid objects. During that period the foamedparticles invariably float to the top of the slurry or at least tend toconcentrate in the upper region thereof.

Foamed polystyrene beads have become widely accepted for mixing withgranulates because of their low density and their low cost. Such beadsusually have sizes ranging from between about 3 to about millimeters indiameter. The head size is too great for direct incorporation in thegranulates since such large beads would noticeably weaken the hardenedgranulate. Consequently, the beads were reduced in size by cutting themwith sharp blades of knives. The cuts were clean and essentially planarand damaged a minimum number of the foamed bead cells. Heretofore thiswas assumed to be desirable, giving the cut beads a generally neat andclean appearance. As will become more apparent hereinafter thiscontributed heavily to the problems encountered in attempts to evenlydistribute such foamed particles in the slurry to decrease the densityof the finally dehydrated granulate.

SUMMARY OF THE INVENTION The present invention provides a method whichallows the equal distribution of low-density foamed particles throughouta slurry. Briefly, the method comprises the steps of mixing granularmaterials to form a slurry and shredding closed-cell, foamed polystyrenebeads into particles so that a substantial portion of the cells of eachparticle are open. The particles are introduced into the slurry andmixed to evenly distribute them throughout the slurry. The slurrypenetrates open cells of the particles and causes an increase in theparticle density to prevent flotation of the particles and maintain theeven particle distribution.

The particles are preferably shredded from foamed polystyrene beads byplacing the beads between relatively moving tearing surfaces havingsawtoothlike serrations. The tearing surfaces are defined bysubstantially circular, opposing surfaces rotating in opposingdirections and at differing speeds. The shredded particles are screenedto remove excessively large particles.

The shredded particles have nonplanar, randomly distributed and unevenexterior surfaces and ragged ridges so that a substantial number of thetheretofore closed foam cells are opened. When mixed with the slurry theincreased density of the foamed particles causes a correspondingdecrease in the buoyancy forces biasing them upwardly. If a sufficientnumber of cells is penetrated with the slurry the buoyancy of theparticles ceases, or becomes so small that the usually high viscosity ofthe slurry prevents the particles from rising.

The heretofore experienced flotation of the particles and their unevendistribution throughout the slurry and the subsequently dehydratedgranulate object are eliminated. As more fully set forth in theabove-referred copending patent application, the physical size of theparticles can be varied according to need. The proportion of foamedparticles in the slurry, and the finished dehydrated granulate object,is of course dependent upon the desired reduction in the density of theobject. That density reduction is a function of the total proportionalvolume occupied by the particles and a result of the removal of slurryfrom the open cells during and after the dehydration of the slurry.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic frontelevational view, with parts broken away, of a shredding apparatus forthe formation of shredded, open-cell foam particles;

FIG. 2 is an enlarged elevational view, in section, and is taken on line2-2 of FIG. I;

FIG. 3 is a fragmentary, enlarged plan view, in section, of theintermeshing tearing surfaces of the apparatus illustrated in FIG. I andis taken on line 3-3 ofFIG. 1;

FIG. 4 is a schematic flow diagram of the method of the presentinvention; and

FIG. 5 is a view of a board constructed of a granulate material andshowing parts of the board in section to illustrate the distribution oflow-density foam particles throughout the board.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 through 3,a shredding machine 8 comprises an upright housing 10 defined by a basesection 12 and a cover 14 demountably secured to the top of the basesection. A pair of intermeshing shredder rolls 16 are rotatably mountedand disposed interiorly of the housing and actuated by drive means I8. Achute 20 is secured to cover 14 and positioned substantially verticallyabove the median between the two shredder rolls, The base sectionincludes a collector funnel 22 beneath the rolls that terminates in apassageway 24 leading into a suctionside 26 of an air blower 28. Theimpeller of the blower is also driven by drive means 18. The pressureside of the blower is connected to a conduit 30 terminating at theexterior of housing 10 in a connection flange 32.

In operation particles to be shredded enter through chute 20, areshredded or torn by the coaction of the shredder rolls 16, are collectedby funnel 22 and fed to the suction side 26 of blower 28 for transportto a point of use as more fully described hereinafter.

THe shredder rolls are preferably of identical construction and eachcomprises a shaft 34 rotatably mounted in journal bearings 36 secured tothe exterior of housing 10 in a conventional manner. One side of theshaft includes an annular ring 38 while another side of the shaftincludes a threaded portion 40. Both the ring and the threaded portionare inward of the shaft extremities which extend through the journalbearings. A multiplicity of large and small diameter, circulardisc-shaped tear plates 42 and 44, respectively, are alternatinglyspaced over the length of shaft 34 between ring 38 and threaded portion40. The tear plates are spaced apart by spacers 46 a distance aboutequal to or slightly greater than the thickness of the tear plates. Theperiphery of the tear plats includes regularly spaced, transverse andgenerally tooth-shaped serrations 48 which have a depth of between aboutone sixty-fourth to about three-sixteenths of an inch, the preferreddepth range being between about one-sixteenth to about one-eighth of aninch for the shredding of foamed polystyrene beads as more fullydescribed hereinafter.

Referring particularly to FIGS, 1 and 3, the actual spacing betweenshafts 34 of the shredder rolls is slightly greater than the combinedradii of the small and the large diameter tear plates 42 and 44 but isless than the combined distance of the radii of two large tear plates 42so that the tear plates of the two shredder rolls overlap (as best shownin FIGS. 1 and 3) and the tear plates interlace. There remains a narrowgap 50 between the tear surfaces 52 of opposing tear plates of the twoshredder rolls. The magnitude of the gap is a function of the desiredsize of the shredded particles. For the shredding of foamed polystyrenebeads having a density of between about 0.2 and about 0.5 pounds percubic foot, an expanded bead size of between about one-fourth to aboutthree-fourths inch diameter. and a desired shredded maximum particlesize of about three-sixteenths of an inch, gap 50 has a width of aboutone thirty-secondth inch.

Referring again to FIGS. 1 through 3, a screen 54 is placed beneathshredder rolls l6 and is secured to sidewalls of housing base section 12in a conventional manner as with threaded bolts. Generally, the screenhas a double-crescent shape (as shown in FIG. 1) and is defined by acenter ridge 56, a first screen section 58 between the center ridge anda point 60 about vertically below the axis of shaft 34, and a secondscreen section 62 extending from point 60 to housing base section 12.

The first screen section has a circular configuration with the center ofthe circle being the axis of the corresponding shredder shaft 34 so thatthe screen section is parallel to the tear surfaces of the tear plates42, 44. The radius of the first screen section is such that the spacingbetween the section and the tear surfaces is in the range of aboutone-sixteenth inch plus the maximum desired average dimension of theshredded particles or less. In the above example in which polystyrenefoam particles are shredded to a maximum dimension of aboutthree-sixteenth inch the spacing between the tear plate tear surfaces 52and the first screen section 58, in a radial direction, is aboutone-sixteenth inch.

Tl-le second screen section is excentric with the tear plates and thespacing, in a radial direction, between the tear surfaces and the secondscreen section increases gradually and continuously from adjacent point60 to the end of the second screen section. The maximum spacing betweenthe tear surfaces and the end of the second section is not critical.

The screen as such may be constructed of a variety of materials and hasmesh or screen openings which permit the passage of the desired particlesizes and prevent particles having excess dimensions from passing thescreen. It is presently preferred to construct the screen of stamped-outsheet metal which lends itself readily to forming to give it the desiredshape. If convenient, other materials, such as wire mesh, can beemployed.

The dimensioning and shaping of the screen 54 is important to preventshredded particles from clogging the space between the tear surfaces andthe screen which can render the shredder inoperable. Contrary to theexpected effect, an increased in the spacing between the tear surfacesand the screen beyond the above-stated range leads to an increasedtendency of clogging. The exact dimensionality of the spacing betweenthe tear surfaces and the first screen section 58 is further a functionof the material being shredded and may require periodic adjustments ofthe spacing.

To enable the ready transport of oversized shredded particles away frombeneath the shredder rolls the second screen sections 62 open up.Oversize shredded particles incapable of passing through the screen arethereby recirculated by the shredder rolls (as described below) into theupper space of housing cover 14 for reshredding. Waste of oversizeparticles is prevented and the recirculation and reshredding isaccomplished without additional feeding mechanisms and the like.

Referring to FIGS. 1 and 3, drive means 18 is schematically illustratedand comprises a relatively small diameter pulley 64 mounted to one ofthe extremities of the left-hand shredder shaft 34 (as seen in FIG. 1),a relatively large diameter pulley 66 mounted to the extremity of theright-hand shredder shaft and a pulley 68 mounted to the extremity ofair blower shaft 29 on the side of housing so that it is aligned withpulley 64. A pair of axially spaced idler pulleys 70, 71 areinterconnected and mounted on the exterior of housing 10. Each idlerpulley is aligned with one of the shredder pulleys 64, 66.

A conventional electric motor 72 is mounted to a support plate 74 andincludes a pulley 76 over which a belt 78 is looped. Belt 78 is furtherlooped over one of the idler pulleys 70, blower pulleys 68 and theleft-hand, small diameter shredder roll pulley 64. A second belt 80 islooped over the second idler pulley 71 and the right-hand, largediameter shredder roll pulley 66. The electric motor is hooked up sothat its pulley rotates in a clockwise direction whereby the left-handshredder roll also rotates in a clockwise direction and the right-handshredder roll (as seen in HO. 1) rotates in a counterclockwisedirection. Materials being shredded and entering the shredding machine 8through chute 20 are thereby drawn into gap 50 between tear surfaces 52.

Aside from rotating in opposing directions it is preferred that the tearsurfaces 52 move at different relative speeds. Consequently pulleys 64,66, 70 and 71 are arranged so that one of the shredder rolls, say theleft-hand roll, rotates at a higher r.p.m. than the left-hand roll. In apresently preferred embodiment of the invention the pulleys are arrangedso that the relative speed differential between the tear surfaces, andtherefor the rpm. differential between rolls, is between about l:l,5 toabout 1:6, with the preferred speed differential being about 1:4

Turning now to the operation of the shredding apparatus, with particularreference to the shredding of the above-mentioned foamed polystyrenebeads, the beads enter through chute 20 and fall gravitationally intospace 82 between and above the two shredder rolls [6. Serrations 49 ofthe tear plates 42, 44 grasp the beads and pull them downwardly. Due tothe speed differential of the tear surfaces 52 the beads are shreddedinto small particles 84 (shown in FIG. 5) in gap 50 between the tearsurfaces. The movement of the tear surfaces transports the particlesdownwardly until they contact screen 54. Those particles which aresmaller than the screen openings fall through the openings and henceunto collector funnel 22. The suction at suction side 26 of air blower28 enhances the passage of those particles through the screen and theirmovement towards the blower. Shreaded particles which are larger, i.e.which have a dimension greater than the maximum dimension of the screenopenings, are prevented from passing the screen. They remain on theupper surface of the screen and are transported in the direction ofrotation of the shredder rolls 16 towards the second screen sections 62.This removal of the excessively large particles is aided by directcontact between serrations 48 and such particles and by air movements orcurrents in the vicinity of the tear plate peripheries caused by therelatively high speed of the rolls. Thus, the oversize particles are ineffect blown into the upper portion of housing cover 14 and into space82 from where they are recycled through the shredder rolls forreshredding and size reduction.

The shredded particles have an irregular configuration, that is theirouter surfaces are on the whole nonplanar, randomly distributed anduneven. The particles include ragged ridges or edges and tears extendingfrom outer surfaces towards the interior or center of the particles.Thus, the surface area of the particles (which includes surfaces causedby the above referred to tears) is relatively large, as compared to theparticle volume, and the surfaces intersect a substantial number ofcells to thereby open the cells to the exterior.

Referring to F IGS. 4 and 5, a particularly advantageous use of theparticles is in the manufacture of granular objects, such as a board 86formed by removing the liquid component from a slurry formed betweengranulates and the water. Generally such liquid removal involves thedehydration of water from the slurry and/or chemical reactions betweenthe granulates and the water.

The granulates may comprise cement particles, sand, gypsum particles andthe like, most commonly referred to as building materials. Suchgranulates have a high density and, therefore, high weight which oftencomplicates their handling and increases their transportation costs. lnaccordance with the present invention the rate or density of suchobjects is reduced by including therein large numbers of the earlierdescribed lowedensity, open-cell foam particles or beads 84.

The foam particles as such distract from the strength of the board sothat they must be evenly distributed throughout the board volume.Concentrations of the foamed particles in certain portions of the boardvolume are therefore highly undesirable. Such concentrations are avoidedsince the shredded particles 84 have large numbers of open cells. Theshredded foam particles are mixed with the slurry by agitating theslurry to obtain an even distribution of the particles. The slurry andparticularly the liquid phase thereof (i.e. the water) enters open cellsof the foamed particles and thereby increases the density of theparticles substantially so that they lose all, or at least the majorportion of their buoyancy, and are prevented from rising towards the topof the slurry. Consequently, the foamed particles penetrated by theslurry remain evenly distributed throughout the slurry during thepreparation of the slurry as well as during the slurry dehydration.

During the dehydration of the slurry water is being removed from betweenthe granulates and from within the open cells of the foam particles 84that have been penetrated by the slurry. Since the volume of each foamparticle remains constant their density is thereby decreased whichcauses a proportional decrease in the density of the finish foamed anddehydrated object.

As already briefly mentioned a major use of the objects is in thebuilding industry, such as in the form of gypsum boards, in suchapplications it is virtually essential that all materials are at leastfire resistant. Although various foam materials can be used it ispresently preferred to use polystyrene, and particularly aerylonitrilestyrene copolymers for the foamed beads since that is a fire-resistantmaterial and enhances the safety of the low-density gypsum boards. Suchfoam materials has the further advantage that the foamed beads can nowbe obtained at relatively low costs in densities as low as 0.2 pound percubic foot.

What is claimed is:

l. A granular material formed from a slurry including granulates and afluid by removing the fluid from the slurry, the material comprising: asolid object defined by the granules and a multiplicity of closed-cellpolystyrene foam particles substantially evenly distributed throughoutthe object and having dimensions substantially less than a minimumdimension of the object, the foamed polystyrene having a density of nomore than about 0.5 pound per cubic foot, the particles havingnonuniform shapes defined by nonplanar, randomly distributed exteriorsurfaces intersecting said opening a plurality of foamed polystyrenecells for contacting the cells with the slurry during the manufacture ofthe object, at least some of the surfaces further terminating in aplurality of ragged edges to increase the number of open polystyrenecells to more intimately contact the particles with the slurry andprevent particle concentrations at portions of the object, whereby thedensity of the object is less than the density of the granules withoutsubstantially compromising the strength of the object.

2. A building board having a thickness substantially less than surfacedimensions of the board, comprising: a substrate of solidified granularmaterial and, evenly distributed throughout the thickness of thesubstrate and over substantially the full surface area of the board, amultiplicity of closed cell foam particles constructed of a foammaterial having a density no more than about 0.5 pound per cubic foot,the particles having maximum dimensions less than the board thicknessand having nonuniform shapes defined by nonplanar, randomly distributedexterior surfaces intersecting a plurality of cells and opening suchcells to the exterior for contacting interior portions of the particleat least during manufacture of the boards with substances having adensity substantially greater than the density of the foam material tothereby prevent excessive particle buoyancy, a resulting particleconcentration at portions of the board, and a weakening and reduction ofthe homogsne i ty f the board.

2. A building board having a thickness substantially less than surfacedimensions of the board, comprising: a substrate of solidified granularmaterial and, evenly distributed throughout the thickness of thesubstrate and over substantially the full surface area of the board, amultiplicity of closed cell foam particles constructed of a foammaterial having a density no more than about 0.5 pound per cubic foot,the particles having maximum dimensions less than the board thicknessand having nonuniform shapes defined by nonplanar, randomly distributedexterior surfaces intersecting a plurality of cells and opening suchcells to the exterior for contacting interior portions of the particleat least during manufacture of the boards with substances having adensity substantially greater than the density of the foam material tothereby prevent excessive particle buoyancy, a resulting particleconcentration at portions of the board, and a weakening and reduction ofthe homogenuity of the board.